Procrustes' Bed

Procrustes' Bed

Posted by Al Sekela (A) on April 24, 2010 at 15:32:56

In Reply to: Yes about those Parallel Networks... posted by Maxamillion on April 24, 2010 at 07:11:52:

Your analysis is correct as long as the goal is only to match the cable impedance to the resistor.

However, as I mentioned below, the capacitors also have their own self-resonance issues.

By experience, I've found it better to isolate the multiple capacitors from each other by placing each one in series with two resistors, one on each side. The sum of the two resistors is the "R" to which we are attempting to load the output circuit of the amplifier and cable.

This does raise the additional question of whether the self-bypassed capacitor designs suffer from intractable internal resonances. I don't know.

Keep in mind the large difference between typical cable impedance and the ten ohms Walker uses in the High Definition Links. The lower impedance may be better in cases of amps with marginal stability at ultrasonic frequencies. If the tweeters do not provide a resistive load over a frequency range well above that in which the amp's feedback network is active, the R-C filters would give a great benefit by stabilizing the amp, and the actual resistance value would not be that important. However, if the amp is stable and cable resonances are the main issue, then matching cable impedance would be more beneficial.

There is plenty of opportunity here for further investigation.

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Follow Ups Full Thread

Topic - Characteristic Impedance and RC Filters - Maxamillion 11:04:37 04/23/10 (17)

RE: Just use a resistor. - rick_m 14:10:20 04/24/10 (0)

Yes, but... - Al Sekela 14:40:56 04/23/10 (13)

Yes about those Parallel Networks... - Maxamillion 07:11:52 04/24/10 (11)

Procrustes' Bed - Al Sekela 15:32:56 04/24/10 (8)

I'm easily confused.... - rwiley 21:51:56 04/25/10 (7)

Yes, that's correct, but - Maxamillion 05:36:13 04/26/10 (6)

I've had good results with... - rwiley 08:00:30 04/26/10 (1)

RE: I've had good results with... - Maxamillion 13:31:47 04/26/10 (0)

Without the theory, in practice - bartc 06:15:09 04/26/10 (3)

Thanks, Bart. Have you tried... - Maxamillion 07:35:05 04/26/10 (2)

Yes, Max, I tried that too - bartc 07:41:29 04/26/10 (1)

I will try multiple combos - Maxamillion 08:30:32 04/26/10 (0)

That is a nature of capacitors after all... - Tweekeng 13:21:15 04/24/10 (1)

RE: That is a nature of capacitors after all... - Maxamillion 13:50:38 04/24/10 (0)

RE: Yes, but... - Maxamillion 19:31:40 04/23/10 (0)

Applies only to R-C filters on SPEAKER cables - bartc 11:22:38 04/23/10 (1)

RE: Applies only to R-C filters on SPEAKER cables - Jack D II 13:14:30 04/27/10 (0)

Follow Ups

Procrustes' Bed - Al Sekela 15:32:56 04/24/10 (8)

I'm easily confused.... - rwiley 21:51:56 04/25/10 (7)

Yes, that's correct, but - Maxamillion 05:36:13 04/26/10 (6)

I've had good results with... - rwiley 08:00:30 04/26/10 (1)

RE: I've had good results with... - Maxamillion 13:31:47 04/26/10 (0)

Without the theory, in practice - bartc 06:15:09 04/26/10 (3)

Thanks, Bart. Have you tried... - Maxamillion 07:35:05 04/26/10 (2)

Yes, Max, I tried that too - bartc 07:41:29 04/26/10 (1)

I will try multiple combos - Maxamillion 08:30:32 04/26/10 (0)

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